1. Field of the Disclosure
The disclosure relates to the development of new and improved microwave plasma assisted reactors, for example chemical vapor deposition (MPCVD) reactors. Relative to conventional microwave plasma assisted reactors, the reactors according to the disclosure operate over larger substrate areas, operate at higher pressures, and operate at higher discharge absorbed power densities with the goal toward increased diamond synthesis rates (carats per hour) and increased deposition uniformity.
2. Brief Description of Related Technology
Early investigations of chemical vapor deposition (CVD) of diamond employed low power density microwave discharges/reactors (i.e., <5 W/cm3) that were operated within the low-pressure regime (i.e., 20 Torr to 100 Torr) and used 1%-5% CH4/H2 input gas mixtures [1, 2]. Both polycrystalline and single crystal films were synthesized with deposition rates that increased from less than 1 μm/h at very low methane concentrations (<1%) to a maximum of a few micron/hour as methane concentrations were increased to 5%. However, high-quality films could only be produced under low methane input conditions (<1%) and, as a result, diamond growth rates were very low (i.e., less than about 1 μm/h). Attempts to increase the growth rate by increasing the input methane concentrations led to the formation of defects such as secondary nucleation and unepitaxial crystallites. While these results were of scientific interest [2], the very low growth rates limited the commercial potential of microwave plasma assisted CVD (MPCVD) synthesis of diamond. Thus, in the mid 1990's, an important scientific and engineering challenge and opportunity that remained unsolved was to discover and develop diamond synthesis methods that dramatically increase the deposition rates while still producing excellent crystalline quality.
During the mid 1990's and early 2000's, several research groups [3, 5-7] searched for improved diamond synthesis methods. Their experiments, which synthesized both polycrystalline and single crystalline materials, utilized high power density (i.e., 50 W/cm3 to 100 W/cm3) microwave discharges operating at moderate pressures between 100 Torr and 180 Torr. Good quality polycrystalline diamond (PCD) was deposited at 4 μm/h to 10 μm/h [6-7] and single crystalline diamond (SCD) was produced at rates of 50 μm/h to 100 μm/h with the addition of nitrogen to enhance the deposition rate [3, 5]. These growth rates were higher by a factor of 5 to 100 times than the growth rates for good quality CVD-synthesized diamond that was obtained in the early 1990's using low pressure microwave discharges.
U.S. application Ser. No. 12/381,270 to Asmussen et al., incorporated herein by reference, relates to a microwave plasma deposition process and apparatus for producing diamond, preferably as single crystal diamond (SCD). The process and apparatus enables the production of multiple layers of the diamond by the use of an extending device to increase the length and the volume of a recess in a holder containing a SCD substrate as layers of diamond are deposited.
Objects
One of the objects is to provide an apparatus and methods for the microwave plasma assisted deposition of diamond that are able to provide both increased deposition rates and excellent crystalline quality for polycrystalline and single crystal diamond. These and other objects may become increasing apparent by reference to the following description.